1. Field of the Invention
The present invention is related to a defocus calibration module, and more particularly, to a defocus calibration module applied in a light-sensing system.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a conventional light-sensing system 100. The light-sensing system 100 is utilized for sensing a measured object MO so as to generate a sensed image SIM. The light-sensing system 100 includes a light-emitting component 110, a focusing component 120, and an image sensor 130. The light-emitting component 110 emits a detecting light LD to the measured object MO, so that the measured object MO generates a reflecting light LR. The image sensor 130 generates a sensed image SIM according to the reflecting light LR. The focusing component 120 is utilized for focusing the reflecting light LR to the image sensor 130. In FIG. 1, m represents the magnification of the focusing component. The front focal distance and the back focal distance of the light-emitting component 120 are D and mD, respectively. The front focal surface and the back focal surface of the focusing component 120 are SUF and SUR, respectively. The image sensor 130 is disposed on the back focal surface SUR of the focusing component 120. A substrate 101 is disposed on the front focal surface SUF of the focusing component 120, and the distance between the substrate 101 and the focusing component 120 is the predetermined distance D (that is, the front focal distance D of the focusing component 120). When the measured object MO touches the substrate 101, it represents the length of the distance between the measured object MO and the focusing component 120 is equal to the length of the front focal distance D of the focusing component 120. Provided that the length of the distance between the image sensor 130 and the focusing component is also equal to the length of the back focal distance mD of the focusing component 120, the reflecting light LR is exactly focused on the image sensor 130 so that the image sensor 130 can generate a clear sensed image SIM. However, when the light-sensing system 100 has an assembling error, it is possible that the length of the distance between the image sensor 130 and the focusing component 120 is not equal to the length of the back focal distance mD of the focusing component 120, or the length of the distance between the substrate 101 and the focusing component 120 is not equal to the length of the front focal distance D of the focusing component 120. In addition, it is possible that the measured object MO does not touch the substrate 101 when the measured object MO forms image on the image sensor 130. In this way, the reflecting light LR generated by the measured object MO can not be exactly focused on the image sensor 130, so that the sensed image SIM generated by the image sensor 130 is unclear.